The present invention relates generally to fuel systems for internal combustion engines, and more particularly to an improved fuel supply system for an internal combustion engine utilizing hydrogen or natural gas for fuel.
Internal combustion engines in cars and trucks may account for as much as about one-third the pollution emitted into the environment. Internal combustion engines used in trains, boats, ships, airplanes, factories, power plants, and the like add substantially to the pollution. Vehicles utilizing alternate sources of fuel such as natural gas, ethanol, methanol, hydrogen, electricity, solar power, have been developed for reducing environmental pollution and utilizing natural resources more efficiently, but generally have short operating range and long refueling times. Also, it may be illusory to characterize electric vehicles as benefiting the environment because many electric power plants typically use more fossil fuel in generating the electricity for charging an electric vehicle than the vehicle would burn using an ordinary internal combustion engine. Automobile manufactures have made significant progress in development of alternate fuel vehicles, but limited operating range and long refueling times remain significant problems.
The invention described herein solves or substantially reduces in critical importance problems with prior alternate fuel systems by providing a constant pressure, variable volume pressure vessel system for the storage of alternate fuel sources aboard cars, trucks, trains, boats, ships and airplanes, and for use in factories, power plants and the like using internal combustion engines. The system is configured to maintain constant pressure in the fuel vessel regardless of the quantity level and without any electrical assistance. By maintaining a constant pressure, the saturation temperature of any alternate fuel can be controlled and held somewhat higher than ambient temperatures so that none of the liquefied fuel will be allowed to flash. The ambient and saturation temperatures are held proportional, regardless of ambient temperature, so the system will work the same in all climates. In this system, the fuel is introduced into the system as a liquid. With other existing pressure vessels, constant pressure is not maintained and thus, saturation temperatures begin falling below ambient temperatures as the quantity of fuel in the system decreases due to the decrease in pressure. Consequently, liquefied fuel being contained by other such vessels will transform from a sub-cooled to a saturated liquid, flash from a saturated liquid into a saturated vapor, and then transform from a saturated to superheated vapor, while remaining at an almost constant temperature.
The invention may benefit any power plant system using an internal combustion engine and may be adapted to function as a static stowage vessel for volatile liquefied alternate fuels such as hydrogen and natural gas at ambient temperature and to transform them into gases prior to dispensing without electrical assistance. The invention may also provide ultra-efficient compressed fluid systems for aircraft and medical oxygen systems and other such uses, and may provide vehicle operating ranges and refueling times favorably comparable to a vehicle using ordinary fuel. Fuels that are gaseous at room temperature and pressure but that can be stowed as a liquid are preferred, such as natural gas and hydrogen, which are relatively inexpensive and abundant. Three separate configurations for the invention are described. The first configuration (least preferable) is used if the pumping station or processing facility can pump the fuel in the liquefied phase either at ambient temperature and high pressure or low pressure and very low temperature. The second configuration (more preferable) can be used only if the liquid fuel is available at ambient temperature and high pressure. The high pressure is required to keep the saturation temperature of the fuel high enough so that ambient temperature can be maintained without the fuel flashing into vapor. Both the first and second configurations utilize an onboard initialization system that stows residual fuel as new fuel is pumped into the system at the processing station. The third configuration (most preferable) also requires the fuel to be at ambient temperature and extremely high pressure, but uses a return feed system to return the residual gaseous fuel back to the processing station while new high pressure, ambient temperature, sub-cooled liquid fuel is pumped into the system. The third configuration is most preferred because the onboard initialization system is not required, which greatly facilitates refueling and significantly reduces the number of components, and consequently the chance of failure, of the system. Note that two methods of transferring the fuel herein described are at high pressure and ambient temperature (herein referred to as "condition 1") or low pressure and extremely low temperature (herein referred to as "condition 2"). The first configuration system can refuel under both condition 1 and condition 2 circumstances, and the second and third configurations can only be refueled under condition 1 circumstances.
Assume two empty pressure vessels identical in volume contain natural gas as a fuel source. Assume further that one of the vessels is filled with compressed natural gas in the gaseous phase and rigidly sealed off so that none can escape, and, still further, that the second vessel is filled with low temperature, ambient pressure, liquefied natural gas and sealed off so that none can escape. If the vessels are allowed to sit for a period of time until their temperatures equal the ambient temperature, the first vessel would still contain compressed natural gas in the gaseous phase and the second vessel would still contain liquefied natural gas. Because of its rigidity, the second vessel does not allow any of the liquefied natural gas to expand as it warmed to ambient, and the saturation temperature rises proportionally with the rise in ambient temperature (as well as pressure) and the natural gas in the second vessel remains in the liquid state even as it warms to ambient and above. The vessel with liquefied natural gas will contain substantially higher mass than the vessel containing compressed natural gas in the gaseous phase.
The invention takes advantage of the physics just described to give the vehicle equal or greater range than other vehicles, by converting the liquefied fuel source into the gaseous phase before transferring it to the engine. This system also makes refueling much faster because the liquefied fuel does not require compressing. The fuel is stowed as an ambient temperature, high pressure, slightly subcooled liquid, expanded several hundred times into a superheated gas, and then combusted as a superheated gas in the engine at about the same volume ratio as ordinary fuels. In condition 2 alternate refueling, because the pressure vessel adjusts its own internal volume at the rate the liquid fuel is drawn from the vessel while maintaining rigidity all the while, the fuel is not allowed to expand in volume as it gradually warms to ambient temperature, which causes the pressure and the saturation temperature to increase correspondingly. Upon stabilizing at ambient temperature, the saturation temperature remains higher than ambient and the fuel remains a subcooled liquid. Ordinary fuel sequencing can take place during this entire cycle. In condition 1 refueling, the temperature will already be ambient, so no temperature change will take place.
It is therefore a principal object of the invention to provide an improved fuel supply system for internal combustion engines.
It is another object of the invention to provide a fuel supply system for internal combustion engines using hydrogen, natural gas or other alternate fuel.
It is yet another object of the invention to provide a fuel supply system for internal combustion engines providing long operating ranges and short refueling times for the vehicle.
It is a further object of the invention to provide a pressure vessel for containing and delivering fuel to an internal combustion engine using hydrogen, natural gas or other alternate fuel.
These and other objects of the invention will be become apparent as a detailed description of representative embodiments of the invention proceeds.